This invention relates to a metal material, mainly to a copper-zinc alloy, i.e., brass, and processes for preparing the same, but the principle of the present invention to be applied is not limited only to brass.
Brass is generally excellent in machinability, good in corrosion resistance and easy in plastic working so that it has been used in an extremely wide field. Among these, a two-phase alloy of xcex1+xcex2 show a large ductility in a hot region (650 to 750xc2x0 C.), and a modification resistance thereof belongs to the lowest group among the metal materials provided for forging.
However, in the characteristics inherently possessed by the material, it cannot be said that research and development of the material itself have been earnestly studied whereas it has an extremely old history. Recently, only a report about ultra-plasticity at brittleness temperature region of an xcex1-type brass has been found. [Tuyoshi Muto et. al.: Nippon Kinzoku Gakkai-shi, 59 (1995), 28]
The present invention has been done in view of the above-mentioned circumstances, and an object thereof is to provide a metal material, brass and a preparation thereof improved in hot working property.
Also, another object of the present invention is to improve hot working property in a plastic working method of a brass material which is representative as metal materials.
Also, another object of the present invention is to provide brass improved in forging property at a low temperature region of 450xc2x0 C. or less and a process for preparing the same, and a plastic working method of a brass material.
A metal material according to the first embodiment of the present invention is a metal material having a microstructure which is formed by dispersing strain by deformation when an external force is received, and said strain energy by the above-mentioned deformation becomes an energy source of recrystallization of said metal microstructure, characterized in that said microstructure contains the first to the third crystals or phases different in hardness. Thus, in the metal material, as compared with microstructure with two-phases, an amount of an interface between different phases increases so that slipping at the interface between different phases effectively acts. According to this, strain is not locally concentrated but dispersed so that a large amount of strain energy is applied to an energy source for recrystallization whereby high hot ductility can be obtained.
It is suitably desired that the above-mentioned first to third crystals are sufficiently made fine so as to disperse the strain caused at the first crystal which is the softest crystal by slipping at the interface between different phases when an external force is applied thereto. When such a constitution is employed, strain can be easily dispersed in cooperation with the slipping at the interface between different phases.
Brass according to the second embodiment of the present invention comprises an apparent Zn content of 37 to 46 wt % and contains Sn of 1.7 to 2.2 wt %. That is, by firstly making the apparent Zn content 37 to 46 wt %, area ratios of xcex2 and xcex3 phases at the recrystallization temperature region can be ensured with certain extents. Here, when the Zn content alone is increased, whereas the xcex2 and xcex3 phases can be ensured, an xcex1 phase cannot be ensured.
Thus, in the brass according to the second embodiment, by adding Sn which is an element having a large Zn equivalent, while ensuring the xcex2 and xcex3 phases at the recrystallization temperature region, the xcex1 phase is also ensured sufficiently whereby an interface slipping between the different phases according to the three phases effectively acts. And it is preferred that the Sn amount is regulated to in the range of 1.7 to 2.2 wt %.
Here, the term xe2x80x9can apparent Zn contentxe2x80x9d is used in the meaning of xe2x80x9c{(B+txQ)/(A+B+txQ)}xc3x97100xe2x80x9d wherein A is a Cu content [wt %], B is a Zn content [wt %], t is a Zn equivalent of the third element (e.g., Sn), and Q is a content of the third element [wt %].
Brass according to the third embodiment of the present invention is brass as a material for effecting plastic working which comprises an apparent Zn content of 37 to 50 wt %, and contains Sn of 1.5 to 7 wt %. Also, more preferably, it is the brass as a material for effecting plastic working comprising an apparent Zn content of 45 to 50 wt %, and containing Sn of 1.5 to 7 wt %.
Brass according to the fourth embodiment of the present invention is brass as a material for effecting plastic working which comprises an apparent Zn content of 37 to 50 wt %, and contains Sn of 3.5 to 7 wt %.
Brass according to the fifth embodiment of the present invention comprises satisfying all the requirements that the microstructure when it is plastic deformed by receiving an external force is a three-phase of xcex1+xcex2+xcex3, an area ratio of the xcex1 phase is 44 to 65%, an area ratio of the xcex2 phase is 10 to 55%, an area ratio of the xcex3 phase is 1 to 25%, average crystal grain sizes of the xcex1, xcex2 and xcex3 phases are 15 xcexcm or less, preferably 10 xcexcm or less, and the above xcex1 and xcex3 phases are present in dispersed states.
Here, when it is a two-phase of xcex1+xcex2, external force-absorption by deformation does not effectively act if the area ratio of the xcex2 phase becomes lower than 30%. However, in the present invention, when the area ratio of the xcex2 phase is lower than 30%, it is defined to be necessarily a three-phase of the xcex1, xcex2 and xcex3 phases. Thus, in this case, slipping at the interface between the different phases effectively acts to realize high ductility.
On the other hand, when the area ratio of the xcex2 phase exceeds 80%, growth and coarsening of crystal grains occur whereby ductility is lowered. In the temperature region coexisting the xcex1, xcex2 and xcex3 phases as in the present invention, the area ratio of the xcex2 phase does not become to such a large value. Also, when the area ratio of the xcex3 phase exceeds 25%, brittleness of the xcex3 phase becomes dominant whereby ductility is lowered. If the area ratio of the xcex1 phase exceeds 65%, optimum ratios of the xcex2 and xcex3 phases cannot be difficultly ensured.
Moreover, the reason why the average crystal grain sizes of the xcex1, xcex2 and xcex3 phases are made 15 xcexcm or less, preferably 10 xcexcm or less, and the above xcex1 and xcex3 phases are present by dispersing is not to concentrated locally but to disperse the strain generated at the xcex2 phase
Brass according to the sixth embodiment of the present invention comprises satisfying all the requirements that the brass has a microstructure of xcex1+xcex2+xcex3 at the recrystallization temperature region, an area ratio of the xcex1 phase at the recrystallization temperature region is 44 to 65%, an area ratio of the xcex2 phase is 10 to 55%, an area ratio of the xcex3 phase is 1 to 25%, average crystal grain sizes of the xcex1, xcex2 and xcex3 phases are 15 xcexcm or less, preferably 10 xcexcm or less, and the above xcex1 and xcex3 phases are present in dispersed states.
Brass according to the seventh embodiment of the present invention comprises satisfying all the requirements that the brass has a microstructure of xcex1+xcex2+xcex3 at the temperature region of 300 to 550xc2x0 C., preferably 400 to 550xc2x0 C., an area ratio of the xcex1 phase at the temperature region is 44 to 65%, an area ratio-of the xcex2 phase is 10 to 55%, an area ratio of the xcex3 phase is 1 to 25%, average crystal grain sizes of the xcex1, xcex2 and xcex3 phases are 15 xcexcm or less, preferably 10 xcexcm or less, and the above xcex1 and xcex3 phases are present in dispersed states.
The brass according to the fifth embodiment of the present invention is brass as a material for effecting plastic working which comprises having at least the xcex3 phase microstructure.
Also, in the brass according to the eighth embodiment of the present invention, an area ratio of the above-mentioned xcex3 phase is preferably 1 to 50 wt %. Also, an average crystal grain diameter of the short axis of the above-mentioned xcex3 phase is preferably 15 xcexcm or less. Also, an average crystal grain diameter of the short axis of the above-mentioned xcex3 phase is more preferably 5 xcexcm or less.
Also, in the brass according to the eighth embodiment of the present invention, an average crystal grain diameter of the short axis of the whole crystal is preferably 15 xcexcm or less. Also, the crystal grain of the above-mentioned xcex3 phase is preferably spheroidal. According to this, forging property of said brass can be improved.
Brass according to the ninth embodiment of the present invention is brass as a material for effecting plastic working which comprises having microstructure of at least a xcex2 phase and a xcex3 phase, an area ratio of the xcex2 phase is 25 to 45 wt %, and an area ratio of the xcex3 phase is 25 to 45 wt %.
Brass according to the tenth embodiment of the present invention is brass as a material for effecting plastic working which comprises having microstructure of at least an xcex1 phase and a xcex2 phase, an area ratio of the xcex1 phase is 30 to 75 wt %, and an area ratio of the xcex2 phase is 5 to 55 wt %.
A process for preparing brass according to the eleventh embodiment of the present invention is a process for preparing the brass having an apparent Zn content of 37 to 46 wt % and containing 1.7 to 2.2 wt % of Sn, which comprises having a step of subjecting to hot extrusion under the conditions of a temperature at the time of extrusion of 300 to 650xc2x0 C., preferably in the range of 530 to 580xc2x0 C., and a reduction of area at the time of extrusion of 90% or more, preferably 95% or more. By applying the step, crystal grains of the xcex1, xcex2 and xcex3 phases at the recrystallization temperature region can be made fine whereby high hot ductility can be realized.
A process for preparing brass according to the twelfth embodiment of the present invention is a process for preparing the brass having a composition of depositing a xcex3 phase at a predetermined temperature and as a material for effecting plastic working, which comprises having a step of making the crystal grain size fine. This step may be a step of making crystal grain size fine by recrystallization at the time of extrusion. It is preferred that the temperature at the time of extrusion is 300 to 650xc2x0 C., and the brass comprises an apparent Zn content of 37 to 50 wt % and contains 0.5 to 7 wt % of Sn. Also, the above step may be a step of recrystallizing at annealing after cold working.
A process for preparing brass according to the thirteenth embodiment of the present invention is a process for preparing the brass having a composition of depositing a xcex3 phase at a predetermined temperature and as a material for effecting plastic working, which comprises having a step of subjecting to extrusion for making the crystal grain size fine, and a step of cooling the extruded brass at a rate of 5xc2x0 C./sec or more. According to this cooling rate, recoasening of crystals once refined can be prevented as little as possible.
Also, in the process for preparing the brass according to the twelfth embodiment of the present invention, the above-mentioned step may be a step of cooling after heating the above-mentioned brass, and during the cooling, a different phase is deposited in the crystal grain to make the crystal grain size fine. This different phase is preferably a xcex3 phase. Also, the xcex3 phase is preferably deposited in a xcex2 phase grain. Also, the cooling rate of the above-mentioned brass is preferably so controlled that the above xcex3 phase is inhibited from depositing at a grain boundary.
Also, in the process for preparing the brass according to the twelfth embodiment of the present invention, the above brass has an apparent Zn content of 37 to 50 wt % and contains 0.5 to 7 wt % of Sn. Also, the composition of the brass is desirably so controlled that the xcex3 phase is inhibited from depositing at a grain boundary.
Also, in the step of cooling the above-mentioned brass after heating in the process for preparing the brass according to the twelfth embodiment of the present invention, it is preferred that, after heating said brass to 650 to 750xc2x0 C. or a temperature region at which the xcex2 phase deposits 50 to 100%, a temperature of said brass is lowered 100xc2x0 C. or more at a cooling rate of 10xc2x0 C./sec or more to cool the brass up to 450xc2x0 C. or lower. The reason why the temperature is lowered 100xc2x0 C. or more is that if it is a temperature lowering of less than 100xc2x0 C., there is a fear that an area ratio of the xcex3 phase cannot sufficiently be ensured.
In the process for preparing the brass according to the twelfth embodiment of the present invention, the above-mentioned brass desirably has an apparent Zn content of 45 to 50 wt % and contains 0.5 to 7 wt % of Sn, or an apparent Zn content of 37 to 50 wt % and Sn of 3.5 to 7 wt %.
Also, in the step of cooling the above-mentioned brass after heating in the process for preparing the brass according to the twelfth embodiment of the present invention, it is preferred that, after heating said brass to a temperature region of 500 to 650xc2x0 C., a temperature of said brass is lowered up to 450xc2x0 C. or lower.
Also, in the step of cooling the above-mentioned brass after heating in the process for preparing the brass according to the twelfth embodiment of the present invention, it is desired to carry out annealing for making the xcex3 phase spheroidal after cooling said brass at a rate of 5xc2x0 C./sec or more. This annealing is desirably carried out at 450xc2x0 C. or lower for 30 minutes or longer. Incidentally, it is desirable to previously subject to cold working to the above-mentioned brass. Also, when the brass is cooled at the rate of 5xc2x0 C./sec or more, if working is carried out during the cooling, the xcex3 phase can be made spheroidal after the cooling.
Also, in the step of cooling the above-mentioned brass after heating in the process for preparing the brass according to the twelfth embodiment of the present invention, said heating may be carried out by subjecting said brass to hot extrusion. The temperature for effecting the extrusion is preferably 300 to 650xc2x0 C. Also, the above-mentioned brass after subjecting to extrusion is preferably transferred to annealing by maintaining at 450xc2x0 C. or lower.
A plastic working method of a brass material according to the fourteenth embodiment of the present invention is a plastic working method of a brass material having a composition of depositing a xcex3 phase at a predetermined temperature and subjecting to a step of making crystal grain size fine, which comprises having a step of plastic working said brass by heating to a temperature of causing recrystallization.
Also, in the plastic working method of a brass material according to the fourteenth embodiment of the present invention, the above step is preferably a step of making crystal grain size fine by recrystallization at the time of extrusion. Also, it is preferred that a temperature of the above-mentioned extrusion is 300 to 650xc2x0 C., an apparent Zn content of the brass is 37 to 50 wt % and it contains 0.5 to 7 wt % of Sn. Also, it is preferred that the above-mentioned step is subjected to annealing after cold working to effect recrystallization.
A plastic working method of a brass material according to the fifteenth embodiment of the present invention is a process for preparing the brass having a composition of depositing a xcex3 phase at a predetermined temperature, which comprises having a step of subjecting to extrusion for making the crystal grain size fine, a step of cooling the extruded brass at a rate of 5xc2x0 C./sec or more and a step of plastic working said brass by heating to such a temperature to cause recrystallization.
Also, in the plastic working methods of brass materials according to the fourteenth and the fifteenth embodiments of the present invention, the temperature to cause the above-mentioned recrystallization may be 300 to 550xc2x0 C. Also, in the plastic working methods of brass materials according to the fourteenth and the fifteenth embodiments of the present invention, at the step of subjecting to plastic working, a xcex3 phase is preferably present in the above-mentioned brass.
Also, in the plastic working method of brass material according to the fourteenth embodiment of the present invention, it is preferred that the above-mentioned step is to effect cooling after heating the above-mentioned brass, and the crystal grain size is made fine by depositing the different phase in the crystal grains during the cooling. Also, the above-mentioned different phase is preferably a xcex3 phase. Also, the above-mentioned xcex3 phase is preferably deposited in a xcex2 phase grain. Also, the above-mentioned brass preferably comprises an apparent Zn content of 37 to 50 wt % and contains 0.5 to 7 wt % of Sn. Also, the cooling rate of the above-mentioned brass is preferably so controlled that the above-mentioned xcex3 phase is prevented from depositing in the grain boundaries. Also, in the step of cooling the above-mentioned brass after heating, it is preferred to heat said brass to 650 to 750xc2x0 C. or a temperature region at which 50 to 100% of a xcex2 phase is deposited, and then a temperature of said brass is lowered 100xc2x0 C. or more at a cooling rate of 10xc2x0 C./sec or more to cool the brass up to 450xc2x0 C. or lower. Also, it is preferred that the composition of the above-mentioned brass is so adjusted that deposition of the xcex3 phase in the grain boundaries is prevented. Also, the above-mentioned brass is preferably an apparent Zn content of 45to 50 wt %, and contains 0.5 to 7 wt % of Sn. Also, the above-mentioned brass is preferably an apparent Zn content of 37 to 50 wt %, and contains 3.5 to 7 wt % of Sn. Also, in the step of cooling the above-mentioned brass after heating, it is preferred that said brass is heated to a temperature region of 500 to 650xc2x0 C. and then said brass is cooled to 450xc2x0 C. or lower. Also, it is preferred that the above-mentioned brass is cooled with a rate of 5xc2x0 C./sec or more and then annealing for making the xcex3 phase spheroidal is carried out. Also, the above-mentioned annealing is preferably carried out at 450xc2x0 C. or lower for 30 minutes or longer. Also, the above-mentioned heating is preferably carried out by hot extruding the above-mentioned brass. Also, the temperature for carrying out the above-mentioned. extrusion is preferably 300 to 650xc2x0 C. Also, it is preferred that the above-mentioned brass subjected to the above-mentioned extrusion is transferred to annealing after maintaining 450xc2x0 C. or lower.
Brass according to the sixteenth embodiment of the present invention comprises having a high hot ductility causing no damage even when a strain of 160% is given with a strain rate of 0.00083/sec at a recrystallization temperature region.
Brass according to the seventeenth embodiment of the present invention comprises satisfying at least one condition of causing no damage even when a strain of 50% is given with a strain rate of 0.00083/sec at a temperature of 450xc2x0 C., causing no damage even when a strain of 25% is given with a strain rate of 0.0083 /sec at a temperature of 450xc2x0 C., or causing no damage even when a strain of 30% is given with a strain rate of 0.083 /sec at a temperature of 450xc2x0 C. In the conventional brasses, there is no material which satisfy such a ductility at such a low temperature.
A plastic working method of a brass material according to the eighteenth embodiment of the present invention is a plastic working method of a brass material having a composition of depositing a xcex3 phase at a predetermined temperature and a step of making a crystal grain size fine is applied to, which comprises having a step of plastic working the above-mentioned brass by heating to 300 to 550xc2x0 C. and a fractional reduction in upsetting height of said brass in this step of 40% or more. Also, the above-mentioned step of making fine is preferably a step of making the crystal grain size fine by recrystallization at extrusion. Also, it is preferred that a temperature of the above-mentioned extrusion is 300 to 650xc2x0 C., an apparent Zn content is 37 to 50 wt %, and Sn is contained in an amount of 0.5 to 7 wt %.
A plastic working method of a brass material according to the nineteenth embodiment of the present invention is a plastic working method of a brass material having a composition of depositing a xcex3 phase at a predetermined temperature, which comprises having a step of extrusion for making a crystal grain size fine, a step of cooling the extruded brass with a rate of 5xc2x0 C./sec or more, and a step of plastic working the above-mentioned brass by heating to 300 to 550xc2x0 C., and a fractional reduction in upsetting height of said brass in the step of plastic working of 40% or more.
Also, in the plastic working method of the brass material according to the eighteenth embodiment of the present invention, it is desired that the above-mentioned step is to cool the above-mentioned brass after heating, and the crystal grain size is made fine by depositing a different phase in the crystal grain during the cooling. Also, the above-mentioned different phase is desirably a xcex3 phase. Also, the above-mentioned xcex3 phase is desirably deposited in a xcex2 phase grain. Also, the above-mentioned brass desirably comprises an apparent Zn content of 37 to 50 wt % and contains 0.5 to 7 wt % of Sn. Also, the cooling rate of the above-mentioned brass is desirably so controlled that the above-mentioned xcex3 phase is prevented from depositing in the grain boundaries. Also, in the step of cooling the above-mentioned brass after heating, it is desired to heat said brass to 650 to 750xc2x0 C. or a temperature region at which 50 to 100% of a xcex2 phase is deposited, and then a temperature of said brass is lowered 100xc2x0 C. or more at a cooling rate of 10xc2x0 C./sec or more to cool the brass up to 450xc2x0 C. or lower. Also, it is desired that the composition of the above-mentioned brass is so adjusted that deposition of the xcex3 phase in the grain boundaries is prevented. Also, the above-mentioned brass may be an apparent Zn content of 45to 50 wt %, and contain 0.5 to 7 wt % of Sn. Also, the above-mentioned brass may be an apparent Zn content of 37 to 50 wt %, and contain 3.5 to 7 wt % of Sn. Also, in the step of cooling the above-mentioned brass after heating, it is preferred that said brass is heated to a temperature region of 500 to 650xc2x0 C. and then said brass is cooled to 450xc2x0 C. or lower. Also, it is preferred that the above-mentioned brass is cooled with a rate of 5xc2x0 C./sec or more and then annealing for making the xcex3 phase spheroidal is carried out. Also, the above-mentioned annealing is preferably carried out at 450xc2x0 C. or lower for 30 minutes or longer. Also, the above-mentioned heating is preferably carried out by hot extruding the above-mentioned brass. Also, the temperature for carrying out the above-mentioned extrusion is preferably 300 to 650xc2x0 C. Also, it is preferred that the above-mentioned brass subjected to the above-mentioned extrusion is transferred to annealing by maintaining 450xc2x0 C. or lower.
A plastic working method of a brass material according to the twentieth embodiment of the present invention is a plastic working method of a brass material having a composition of depositing a xcex3 phase at a predetermined temperature and a step of making a crystal grain size fine is applied to, which comprises having a step of plastic working the above-mentioned brass by heating to 300 to 550xc2x0 C. and a fractional reduction in upsetting height of said brass in this step of 70% or more.* It is desired that the composition of the above-mentioned brass is so adjusted that deposition of the xcex3 phase in the grain boundaries is prevented. Also, the above-mentioned brass may be an apparent Zn content of 45 to 50 wt %, and may contain 0.5 to 7 wt % of Sn. Also, the above-mentioned brass may be an apparent Zn content of 37 to 50 wt %, and contain 3.5 to 7 wt % of Sn. Also, the above-mentioned step of making fine is preferably a step of cooling the above-mentioned brass after heating, and said brass is heated to a temperature region of 500 to 650xc2x0 C. and then said brass is cooled to 450xc2x0 C. or lower.
A plastic working method of a brass material according to 21st embodiment of the present invention is a plastic working method of a brass material subjecting to plastic working by heating the brass at 300 to 550xc2x0 C., and a fractional reduction in upsetting height of said brass at plastic working is 40% or more.
A plastic working method of a brass material according to 22nd embodiment of the present invention is a plastic working method of a brass material subjecting to plastic working by heating the brass at 300 to 550xc2x0 C., and a fractional reduction in upsetting height of said brass at plastic working is 70% or more.
Brass according to the 23rd embodiment of the present invention is a brass having an apparent Zn content of 37 to 50 wt % and containing 0.5 to 7 wt % of Sn, which comprises having a different phase deposited in a crystal grain by cooling said brass after heating, said brass has a xcex3 phase in an amount of 1 to 50 wt %, and an average crystal grain size of a short axis of said xcex3 phase is 5 xcexcm or less.
Brass according to the 24th embodiment of the present invention is a brass having an apparent Zn content of 45 to 50 wt % and containing 0.5 to 7 wt % of Sn, which comprises having a different phase deposited in a crystal grain by cooling said brass after heating, said brass has a xcex2 phase in an amount of 25 to 45 wt % and has a xcex3 phase in an amount of 25 to 45 wt %, and an average crystal grain size of a short axis of said xcex3 phase is 10 xcexcm or less.
Brass according to the 25th embodiment of the present invention is a brass having an apparent Zn content of 37 to 50 wt % and containing 3.5 to 7 wt % of Sn, which comprises having a different phase deposited in a crystal grain by cooling said brass after heating, said brass has a xcex2 phase in an amount of 25 to 45 wt % and has a xcex3 phase in an amount of 25 to 45 wt %, and an average crystal grain size of a short axis of said xcex3 phase is 10 xcexcm or less.
A plastic working method of a brass material according to the 26th embodiment of the present invention is a plastic working method of a brass material subjecting to plastic working by heating the brass material to 300 to 550xc2x0 C., which comprises a dynamic recrystallization being caused in said brass material at the time of the above-mentioned plastic working. Also, at the time of the above-mentioned plastic working, it is preferred that a xcex3 phase is present in the above-mentioned brass material.
A process for preparing brass according to the 27th embodiment of the present invention is a process for preparing brass having an apparent Zn content of 37 to 46 wt % and containing 1.7 to 2.2 wt % of Sn, which comprises having a step of hot working said brass in the range of 300 to 550xc2x0 C. or 400 to 550xc2x0 C. By subjecting to hot working in this temperature region, an optimum ratio of the xcex1, xcex2 and xcex3 phases is ensured at the recrystallization temperature region of said brass so that slipping at the interface during three phases can effectively act. Moreover, by realizing a high hot workability at a low temperature region, it contributes to improve in durability of a working plant. That is, dimensional accuracy at the time of working becomes good and a moldlife becomes long.
A process for preparing brass according to the 28th embodiment of the present invention is a process for preparing brass having an apparent Zn content of 37 to 46 wt % and containing 1.7 to 2.2 wt % of Sn, which comprises having a step of subjecting the above-mentioned brass to hot extrusion under the conditions of a temperature at the extrusion being in the range of 300 to 650xc2x0 C., and a reduction of area at the extrusion being 90% or more, and a step of hot working said brass in the range of 300 to 550xc2x0 C. or 400 to 550xc2x0 C.
A plastic working method of a brass material according to the 29th embodiment of the present invention is a plastic working method of a brass material containing 0.5 to 7 wt % of Sn, which comprises subjecting the plastic working in the range of 300 to 550xc2x0 C.
A plastic working method of a brass material according to the 30th embodiment of the present invention is a plastic working method of a brass material containing 0.5 to 7 wt % of Sn, which comprises said brass material at the plastic working being a temperature of a temperature region which causes recrystallization during working and a temperature region of 550xc2x0 C. or lower.
A plastic working method of a brass material according to the 31st embodiment of the present invention is a method of plastic working a brass material at a temperature region of 300xc2x0 C. or higher or a temperature region of causing recrystallization during working, which comprises a xcex3 phase being present in said brass material at the plastic working. Also, it is preferred that the existing ratio of the above-mentioned xcex3 phase is within the range of 1 to 50 wt %. Also, it is more preferred that the existing ratio of the above-mentioned xcex3 phase is within the range of 25 to 45 wt %, and in the brass material at the above-mentioned plastic working, a xcex2 phase is further present and an existing ratio thereof is 25 to 45 wt %.
A plastic working method of a brass material according to the 32nd embodiment of the present invention is a method of plastic working a brass material at a temperature region of 300xc2x0 C. or higher or a temperature region of causing recrystallization during working, which comprises an xcex1 phase and a xcex2 phase being present in said brass material at the plastic working, and an existing ratio of said xcex1 phase is in the range of 30 to 75 wt % and an existing ratio of said xcex2 phase is in the range of 5 to 55 wt %.
Also, in the plastic working method of brass according to the 31st embodiment of the present invention, it is preferred that an average crystal grain diameter of a short axis of the above-mentioned xcex3 phase is 15 xcexcm or less. Also, it is preferred that an average crystal grain diameter of a short axis of the above-mentioned xcex3 phase is 5 xcexcm or less.
Also, in the plastic working method of the brass material according to the 31st embodiment or the 32nd embodiment of the present invention, it is preferred that an average crystal grain diameter of a short axis in the crystal grain of the above-mentioned brass material is 15 xcexcm or less. Also, it is preferred that crystal grain of the above-mentioned xcex3 phase is spheroidal.
A plastic working method of a brass material according to the 33rd embodiment of the present invention is a method of plastic working a brass material which comprises* the xcex3 phase at room temperature, subjecting to the plastic working of said brass material at a temperature of 550xc2x0 C. or lower.
A plastic working method of a brass material according to the 34th embodiment of the present invention is a method of plastic working a brass material at a temperature region of 300xc2x0 C. or higher or a temperature region of causing recrystallization during working, which comprises a first step of preparing a brass material, a second step of heating said brass material to the above-mentioned temperature region, and a third step of applying plastic working to said heated brass material, and an area ratio of a xcex3 phase in the above-mentioned third step is increased as compared with that in the above-mentioned first step. Also, an area ratio of the xcex3 phase after completion of the second step is preferably increased than that of the above-mentioned first step. Also, it is preferred to further contain, in the above-mentioned first step, a step of heating the above-mentioned brass material to a temperature region higher than the temperature region at which the xcex3 phase deposits, and then, rapidly cooling said brass material. Also, when the above-mentioned brass material is rapidly cooled, it is preferred that a cooling rate passing through the temperature region at which the above-mentioned xcex3 phase deposits is a cooling rate at which deposition of the xcex3 phase is not saturated, more specifically, it is preferably 5xc2x0 C./sec or more. Also, when the above-mentioned brass material is rapidly cooled, it is preferred that a cooling rate passing through the temperature region at which the above-mentioned xcex3 phase deposits is a cooling rate at which no xcex3 phase is deposited, more specifically, it is preferably 15xc2x0 C./sec or more.
A plastic working method of a brass material according to the 35th embodiment of the present invention is a method of plastic working a brass material at a temperature region of 300xc2x0 C. or higher or a temperature region of causing recrystallization during working, which comprises a first step of preparing a brass material, a second step of heating said brass material to the above-mentioned temperature region, and a third step of applying plastic working to said heated brass material, and said brass material in the above-mentioned third step has a finer average crystal grain size as compared with that in the above-mentioned first step. Also, the brass material after completion of the above-mentioned second step preferably has a finer average crystal grain size as compared with that in the above-mentioned first step. Also, it is preferred to further contain, in the above-mentioned first step, a step of heating the above-mentioned brass material to a temperature region higher than the temperature region at which the xcex3 phase deposits, and then, rapidly cooling said brass material. Also, when the above-mentioned brass material is rapidly cooled, it is preferred that a cooling rate passing through the temperature region at which the above-mentioned xcex3 phase deposits is a cooling rate at which no xcex3 phase is deposited, more specifically, it is preferably 15xc2x0 C./sec or more. Incidentally, the reason why the above-mentioned cooling rate is made a rate of not depositing the xcex3 phase is that if it is made a rate (5xc2x0 C./sec or more) at which deposition of the xcex3 phase is not saturated, when the brass material is heated to a working temperature at the above-mentioned second step, the xcex3 phase deposits at the xcex2 grain interface so that there is a possibility of not making the crystal grain fine.